(1) Field of the Invention
The present invention relates to a record/reproduction controlling signal generator with an error preventing circuit having an automatic level control (ALC) circuit. More particularly, the above generator with an error preventing circuit has an automatic level control (ALC) circuit that is made up in the form of simple hardware and synchronizes to a recording point to preclude transient phenomena that may occur when the power to the device is turned on.
(2) Description of the Prior Art
Referring now to the drawings, a conventional automatic level control (ALC) circuit may be described as follows. FIG. 1 is a circuit diagram showing a conventional automatic level control (ALC) circuit. This circuit includes an attenuator 10 that receives and attenuates a recording signal to reproduce it; an amplifier 20 that receives the signal produced from the attenuator 20, then amplifies and reproduces the signal; a comparator 30 that receives the recording signal produced from the amplifier 20 through a non-inverting (+) input terminal and a predetermined reference voltage Vr through an inverting (-) terminal, where the comparator 30 compares the two input signals to produce a detecting signal; a capacitor C1 that charges or discharges the detecting signal produced from the comparator 30 and converts the signal into a direct current to transmit it to the attenuator as attenuating data; a switch SW 60 that connects an output terminal of the comparator 30 to a ground, and where the switch SW 60 also protects the circuit by discharging the abnormal voltage that may occur by transient phenomena when the power is first turned on; an error preventing circuit 40 which is made up of a delay circuit for determining a turn-on time of the switch SW 60; and a record/reproduction controlling signal generating circuit 50 that receives a record/reproduction controlling signal through an external switch labelled in FIG. 1 as R/P SW 70.
The error preventing circuit 40 includes a capacitor C2 that charges voltage through the external voltage current source and determines the time for turning on of the switch SW 60. The circuit 40 also includes a delay circuit 41 that has the function of delaying the turn-on time for the switch SW 60 which is regulated by input from the capacitor C2.
In operation, the comparator 30 detects a signal which is over the reference voltage Vr in this conventional ALC circuit. The signal is converted into a direct current and transmitted as attenuating data to the attenuator 10 during the attenuation of the recording signal to reduce an input signal supplied by the attenuator 10 to the amplifier 20.
The conventional ALC circuit functions without any problems during times of normal operation. However, this ALC circuit generally creates an abnormal voltage at the output of the comparator 30, which is caused by the transient phenomena at the time when power is turned on. To avoid abnormal operation of the attenuator 10 caused by the high voltage of the capacitor C1, the ALC circuit is designed to discharge the voltage of the capacitor C1 at the transient edge by including the error preventing circuit 40.
As shown in FIG. 1, assigning an additional terminal to the circuit and then connecting it to the capacitor C2, which is a time delay means, is a simple way to form the error preventing circuit 40. It is common to use a capacitor that is necessary for another function to also provide this necessary function without resorting to the use of additional terminals and capacitors. The above-mentioned capacitor has the other function of being a ripple-removing filter of power that produces bias voltage or of being a direct current cut-off capacitor for a feedback terminal of an amplifier.
However, there is a time difference between the voltage rise of these terminals and the transient voltage rise of the recording amplifier. Therefore, the anomalous overcharge voltage is not fully discharged unless the delay circuit is designed with considerable precision.
Moreover, when it comes to circuit design, a semiconductor device is represented through simulation by means of a computer-aided design. However, the operation of a component in the computer-simulation of a circuit design is generally different from the actual operation of the circuit. Accordingly, the circuit is subject to frequent modifications of the design in actual practice.